Potential-dependent electrochemiluminescence of luminol in alkaline solution at a gold electrode

Abstract

The behavior of luminol electrochemiluminescence (ECL) at a polycrystalline gold electrode was studied under conventional cyclic voltammetric (CV) conditions. At least six ECL peaks were observed at 0.28 (ECL-1), 0.56 (ECL-2), 0.95 (ECL-3), 1.37 (ECL-4), −0.43 (ECL-5) and 1.00 (ECL-6, a broad wave after the reverse scan from +1.66) V (vs. SCE), respectively, on the curve of ECL intensity versus the potential. These ECL peaks were found to depend on the presence of O 2 and N 2, the pH of the solution, KCl concentration, scan rate, and potential scan ranges. The emitter of all ECL peaks was identified as 3-aminophthalate by analyzing the CL spectra. It is believed that ECL-1 at 0.28 V was correlated to luminol radicals produced by the electro-oxidation of luminol anion and ECL-2 at 0.56 V was caused by the reaction of luminol radical anions with gold oxide formed on the electrode surface. ECL-1 and ECL-2 could be strongly enhanced by O 2 and O 2 − . ECL-3 at 0.95 V was likely to be due to the reaction of luminol radical anions with O 2 oxidized by OH −. ECL-4 at 1.37 V suggested that OH − was electro-oxidized to HO 2 − at this potential and then to O 2 − , which reacted with luminol radical anions to produce light emission. ECL-5 at −0.43 V seems to be due to the reaction of luminol with ClO − electrogenerated at higher positive potential and HO 2 − electrogenerated at negative potential. ECL-6 was attributed to the reaction of luminol radical anions and ClO − electrogenerated at higher positive potential. The results indicated that luminol ECL can be readily initiated by various oxygen-containing species electrogenerated at different potentials, leading to multi-channel light emissions. Furthermore, the present work also reveals that ECL-2 is a predominant ECL reaction route at a gold electrode with higher potential scan rates under CV conditions.